The present invention relates to an automatic heating apparatus, or more in particular to an automatic heating apparatus using a weight sensor and a gas sensor.
Automatic heating apparatuses in which the heating time is automatically regulated find wide applications. An automatic microwave oven, for example, is highly evaluated for its operating convenience and accounts for a considerable share of the microwave oven market. An automatic microwave oven comprises a gas sensor responsive to vapour, steam or various gases generated during the heating of an object to be heated, or a thermistor for measuring the temperature of the air flowing into or from the heating chamber thereof. In any of these types, the manner of heating the object is divided into a number of heating steps according to the type of food involved. For reheating, for instance, the operation is often performed through the actuations of two or three select keys. FIG. 1 is a perspective view of such an automatic heating apparatus, and FIG. 2 is a diagram showing the essential parts of an operating panel for the apparatus. A door 2 adapted to be opened or closed as desired and an operating panel 3 are mounted on the front of a body 1. Various select keys 4 are arranged on the operating panel 3 so that the manner of heating may be selected according to the food involved. For reheating, the shown example has three keys labeled "Cold boiled rice", "Soup" and "Curry/Stew" to enable an appropriate select key to be used according to the type of food. This is due to the fact that if the heating is finished at the time point when water steam or gas has emanated from the food or the surface temperature of the food has reached a predetermined level, the central portion of some food may not be sufficiently heated and therefore must be additionally heated and that the length of time of the additional heating varies with the type of food involved. This relationship is shown in FIG. 3 for a gas sensor responsive to vapour or steam generated from the food. Assume that T.sub.1 designates the length of time required to reach the detection point where a predetermined amount of steam is detected. It is recommended that the heating of the cold boiled rice be stopped upon the detection of the steam, and in the case of the soup, an additional heating time of K.sub.1 T.sub.1 is required to be added to the time T.sub.1 to prevent it from becoming lukewarm. Based on experience, K.sub.1 is a constant selected to be about 0.1 to 0.5. Melting food such as curry or stew must be further heated for an additional time of K.sub.2 T.sub.2, where K.sub.2 is determined at about 0.3 to 0.8. In this way, the value K varies with the type of food because steam is generated differently from different foods. For example, some foods exhibit thermal characteristics of low heat conduction or convection, and others generate steam fron only parts thereof. The user, therefore, must select the proper select key depending on the type of food to be heated. Since the menus described on the keyboard usually shows only two or three items, it is necessary to refer to the cuisine book or the like to determine whether a given food can be automatically cooked in the apparatus. When it is desired to reheat macaroni, for instance, the user unfamiliar with the operation can not decide which keys should be used. A market survey has shown that in spite of the frequent use of the reheating function, only a small percentage of users use the automatic mode of reheating. The troublesome operation for selecting the select keys may be one reason for this fact.
The object of the present invention is to obviate this disadvantage of the conventional apparatuses and to provide an automatic heating apparatus which is easy to operate, and in which the plurality of reheating select keys that have so far been used for a plurality of food types are replaced by a single select key.